Because the Equifax credit reports contained so much personal information, including Social Security numbers and financial account information, fraudsters could use the report for reasons including new account fraud, medical identity theft -- using insurance information to have a medical procedure, which can create confusion on the true insured person's medical file for years -- or tax fraud, Levin said.

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Incidents of new account fraud have risen especially quickly, Javelin found, because so much personal information has been compromised in data breaches over time. New account fraud also takes the longest to resolve, said Al Pascual, a senior vice president and research director at the security firm Javelin. "If you don't take steps to actively protect your identity, you're basically playing Russian roulette," Pascual said....

At an absolute minimum, consumers should check their financial accounts, credit reports and credit score frequently, Nazari of Credit Sesame said. But putting a freeze or fraud alert on an account is strongly recommended, he said. Fraud alerts won't prevent fraud from happening, but can let a consumer know when something looks suspicious, and they can follow up with the appropriate financial institution after.